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Abstract:

Provided are a heat releasing material for an electronic device being
manufactured by the junction of a metal impregnated carbon composite
material on a copper or aluminum substrate with reduced warpage; and a
method for manufacturing the heat releasing material. A metal
substrate/metal impregnated carbon composite material structure,
characterized in that it comprises a metal substrate comprising a metal
sheet, plate or block and, being joined on the metal substrate via a
brazing material, a metal impregnated carbon composite material having a
thickness of 0.1 mm to 2 mm; and a method for manufacturing the metal
substrate/metal impregnated carbon composite material structure,
characterized in that it comprises a step wherein a brazing material is
caused to be present between the metal substrate and the metal
impregnated carbon composite material, and they are kept at a temperature
of 500° C. or higher and under a pressure of 0.2 MPa or more and
then cooled.

2. The metal substrate-metal impregnated carbon composite structure
according to claim 1, wherein the metal impregnated carbon composite has
a thickness of 0.1 to 2 millimeters.

3. The metal substrate-metal impregnated carbon composite structure
according to claim 1 or 2, wherein a metal of the metal substrate is
copper, aluminum, or alloys of these.

4. The metal substrate-metal impregnated carbon composite structure
according to claim 1 or 2, wherein the metal substrate is in the shape of
a sheet, plate material, or block.

5. The metal substrate-metal impregnated carbon composite structure
according to claim 1 or 2, wherein warp on the metal impregnated carbon
composite side of the metal substrate-metal impregnated carbon composite
structure is controlled to 0.15 millimeters or less on the diagonal line
of 50 millimeters×50 millimeters.

6. The metal substrate-metal impregnated carbon composite structure
according to claim 1 or 2, wherein the constituent of a covering layer of
the metal impregnated carbon composite is ceramics or a metal foil.

7. The metal substrate-metal impregnated carbon composite structure
according to claim 1 or 2, wherein ends of the metal impregnated carbon
composite are embedded in the metal substrate.

8. The metal substrate-metal impregnated carbon composite structure
according to claim 1 or 2, wherein a metal of the metal impregnated
carbon composite is magnesium, aluminum, copper, silver, or alloys of
these metals.

9. The metal substrate-metal impregnated carbon composite structure
according to claim 1 or 2, wherein the properties in any one direction of
three axial directions of the metal impregnated carbon composite are a
thermal conductivity of 100 W/mK or more, a thermal expansion coefficient
of 4.times.10.sup.-6/degrees centigrade to 15.times.10.sup.-6/degrees
centigrade, and a Young's modulus of 25 GPa or less.

10. A production method for a metal substrate-metal impregnated carbon
composite structure that comprises a metal substrate and a metal
impregnated carbon composite brazed and soldered onto an upper surface of
the metal substrate, comprising the steps of; interposing a brazing
material between the metal substrate and the metal impregnated carbon
composite; heating and holding these at a temperature equal to or more
than the melting point of the brazing material; and then cooling these at
least under pressurization.

11. The production method for a metal substrate-metal impregnated carbon
composite structure according to claim 10, wherein the metal impregnated
carbon composite has a thickness of 0.1 millimeters to 2 millimeters.

12. The production method for a metal substrate-metal impregnated carbon
composite structure according to claim 10 or 11, wherein the pressurizing
condition is 0.2 MPa or more.

13. The production method for a metal substrate-metal impregnated carbon
composite structure according to claim 10 or 11, wherein the holding
temperature is 350 degrees centigrade or more.

Description:

TECHNICAL FIELD

[0001] The present invention relates to a junction structure of a metal
substrate and a metal impregnated carbon composite (MICC) and a
production method for this junction structure, and more specifically, to
a structure obtained by joining a metal substrate made of copper or
aluminum and a metal impregnated carbon composite by using a brazing
material, an IC (semiconductor integrated circuit) package using this
structure or an electronic circuit including this IC package, and a
production method for the structure.

BACKGROUND ART

[0002] The energy density in a high-speed and high-integration
semiconductor is very high, and to efficiently exhaust the heat, a method
in which the heat is quickly diffused and exhausted by using a heat
radiation substrate made of aluminum or copper with excellent thermal
conductance is suitable.

[0003] However, although the thermal expansion coefficient of ceramics to
be used for the semiconductor or the circuit board of the semiconductor
is 4 to 8×10-1 degrees centigrade, the thermal expansion
coefficients of aluminum and copper are as high as 16 to
23×10-6/degrees centigrade, so that high heat stress occurs in
the joining layer due to this difference in thermal expansion coefficient
and it is not easy to join these materials together.

[0004] A first measure against this is to select a heat radiation
substrate with a smaller thermal expansion coefficient, and
conventionally, materials obtained by combining silicon carbide,
tungsten, molybdenum, etc., having small thermal expansion coefficients
with copper or aluminum metal with a high thermal conductivity, and to
adjust the thermal expansion coefficient to 7 to
10×10-6/degrees centigrade are provided. However, as a problem
with these materials, the thermal conductivities of these materials are
20% or more lower than that of copper or aluminum alone such that the
thermal conductivity of a material using copper is 200 to 300 W/mK and
the thermal conductivity of a material using aluminum is 150 to 200 W/mK,
and Young's modulus of the substrate is high, so that in the case of
junction with silicon or aluminum nitride, etc., with a thermal expansion
coefficient of about 4×10-6/degrees centigrade, the heat
stress occurring in the joining layer increases, so that joining of a
large area becomes difficult.

[0005] As a second measure, a resin or solder with a low Young's modulus
is used for the joining layer to relax the heat stress to be caused by
the difference in thermal expansion coefficient. However, this has a
drawback in the thermal conductivities of the resin and solder being as
low as 1 W/mK and several tens of W/mK, respectively, and small fracture
strength, so that a thicker joining layer becomes necessary, and as a
result, the thermal resistance of the joining layer increases.

[0006] In addition, disadvantages are also pointed out in that, in the
case of resin, hygroscopic property and thermal resistance are low, and
in the case of solder, the yield stress in a practical temperature range
is low and thermal fatigue easily occurs.

[0007] As described above, in heat radiation systems widely employed in
electronics devices currently, improvement in thermal conductivity in the
joining layer which relaxes or reduces thermal stress caused by a
difference in the thermal expansion coefficient has become an issue.

[0008] In the specification of this application, "thermal stress relaxing
effect" means an effect in that, as known, a stress occurring in a
joining interface of two materials with different thermal expansion
coefficients when joining these is in proportion to the thermal expansion
coefficients of the two materials and the elastic modulus of each
material, so that the stress occurring in a material with a low elastic
modulus becomes smaller, and even materials with greatly different
thermal expansion coefficients can be joined, and can resist thermal
fatigue caused by repetition of heating and cooling.

[0009] In view of these circumstances, previously, the inventor of the
present invention suggested a metal impregnated carbon composite obtained
by pressure-filling or impregnating the insides of pores of a carbon
material such as graphite with a metal (for example, refer to Japanese
Patent No. 3351778). In comparison with the above described material
containing silicon carbide, tungsten, molybdenum, etc., in main
proportions, this metal impregnated carbon composite has a high thermal
conductivity, an equivalent thermal expansion coefficient, and a low
Young's modulus, so that it shows an effect that relaxes thermal stress
occurring in the joining layer of solder, etc., when silicon or ceramics,
etc., is mounted, and it was found that this material improves the above
described problem, however, it also includes disadvantages in that it is
fragile and low in mechanical strength.

[0010] As a measure against this, the inventor of the present invention
tried a method in which a metal impregnated carbon composite with a
thickness of about 1 millimeter that was plated was joined onto a copper
or aluminum substrate by soldering and a semiconductor element was joined
by low-temperature solder thereon, however, the inventor found a problem
in that the thermal expansion coefficient of the metal impregnated carbon
composite was 4×10-6/degrees centigrade through
10×10-6/degrees centigrade, and on the other hand, the thermal
expansion coefficient of copper was 16×10-6/degrees
centigrade, and the thermal expansion coefficient of aluminum was
23×10 -6/degrees centigrade, and these were greatly different,
so that the solder-joined substrate warped to project toward the
composite side, and trouble occurred in the post-process such as mounting
of silicon. Under these circumstances, development of a heat radiation
material with smaller warp and improved strength by applying a carbon
material with a thermal stress relaxing effect has been demanded.

[0011] Patent document 1: Japanese Patent Publication No. 3351778

DISCLOSURE OF THE INVENTION

Object to be Achieved by the Invention

[0012] Therefore, in view of the above described development
circumstances, an object of the invention is to provide a metal
substrate-metal impregnated carbon composite structure which shows a
thermal heat stress relaxing effect by the metal impregnated carbon
composite in a surface for mounting an electronics device such as a
silicon or ceramics substrate with a small thermal expansion coefficient,
and shows values of strength and thermal conductivity close to those of
copper or aluminum of the substrate metal, and has smaller warp, and a
production method for this structure.

Means for Achieving the Object

[0013] Therefore, in order to achieve the object, the inventor of the
present invention conducted an earnest examination, and as a result,
focused on a fact that by joining a metal substrate made of copper or
aluminum and a metal impregnated carbon composite with a specific
thickness under specific conditions and using the low elasticity of the
metal impregnated carbon composite, a metal substrate-metal impregnated
carbon composite structure whose warp is suppressed could be provided,
and then based on this knowledge, arrived at completion of the present
invention.

[0014] Therefore, a first aspect of the invention provides a metal
substrate-metal impregnated carbon composite structure including a
metal substrate and a metal impregnated carbon composite brazed and
soldered onto an upper surface of the metal substrate.

[0015] In addition, a second aspect of the invention provides a production
method for a metal substrate-metal impregnated carbon composite structure
that includes a metal substrate and a metal impregnated carbon composite
brazed and soldered onto an upper surface of the metal substrate,
including steps of interposing a brazing material between the metal
substrate and the metal impregnated carbon composite, and heating and
holding this at a temperature equal to or more than the melting point of
the brazing material, and then cooling this at least under
pressurization.

Effect of the Invention

[0016] According to a metal substrate-metal impregnated carbon composite
structure of the present invention, as described above, when an
electronics device such as a silicon or ceramics substrate with a small
thermal expansion coefficient is mounted on a surface of the metal
impregnated carbon composite, an electronics device radiation substrate
which shows a thermal stress relaxing effect of the metal impregnated
carbon composite and shows values of strength and thermal conductivity
close to those of copper or aluminum of the substrate metal can be
provided. In addition, according to the production method for the
structure of the present invention, by setting joining conditions to a
high temperature and a high pressure, the heat radiation substrate with
reduced warp can be efficiently produced.

BEST MODE FOR CARRYING OUT THE INVENTION

[0017] The present invention relates to a structure including a metal
substrate formed of a metal-made sheet, plate material, or block, and a
metal impregnated carbon composite with a thickness of 0.1 to 2
millimeters brazed and soldered to an upper surface of the metal
substrate, and as a more preferable embodiment, the present invention
includes the following 1) through 5). [0018] (1) An electronics device
heat radiating metal substrate-metal impregnated carbon composite
structure including a metal impregnated carbon composite with a thickness
of 0.1 to 2 millimeters and a copper or aluminum substrate whose upper
surface is joined to the lower surface of the composite via a brazing
material. [0019] (2) An electronics device heat radiating metal
substrate-metal impregnated carbon composite structure including a copper
foil, a metal impregnated carbon composite with a thickness of 0.1 to 2
millimeters whose upper surface is joined to a lower surface of the
copper foil via a brazing material, and a copper or aluminum substrate
whose upper surface is joined to a lower surface of the composite via a
brazing material. [0020] (3) An electronics device heat radiating metal
substrate-metal impregnated carbon composite structure including a metal
impregnated carbon composite with a thickness of 0.1 to 2 millimeters
whose upper surface is joined to a lower surface of a ceramics insulating
substrate of alumina or the like via a brazing material, and a copper or
aluminum substrate whose upper surface is joined to the lower surface of
the composite via a brazing material. [0021] (4) An electronics device
heat radiating metal substrate-metal impregnated carbon composite
structure including a metal impregnated carbon composite with a thickness
of 0.1 to 2 millimeters covered by a metal by housing the composite into
a recess of a copper or aluminum substrate and joining copper or aluminum
foils or substrates to upper and lower surfaces of this composite via a
brazing material. [0022] (5) An electronics device heat radiating metal
substrate-metal impregnated carbon composite structure including a metal
substrate, a metal impregnated carbon composite with a thickness of 0.1
to 2 millimeters whose lower surface is joined to an upper surface of the
metal substrate via a brazing material, and a silicon element whose lower
surface is joined to an upper surface of this metal impregnated carbon
composite via a brazing material.

[0023] As the metal substrate of the metal substrate-metal impregnated
carbon composite structure relating to the present invention, copper,
aluminum, or alloys of these are preferable. The form of the metal
substrate is not especially limited, however, a sheet-like, plate, or
block shape, etc., is adopted. The thickness of the metal substrate can
be arbitrarily determined according to the structure of the electronics
device to which the structure is applied, however, it can be selected in
a range of 0.5 to 5 millimeters, preferably, in a range of 1 to 3
millimeters.

[0024] As a brazing material that is a component of the structure, a hard
solder with a melting point of 450 degrees centigrade or more and a soft
solder with a melting point of 450 degrees centigrade or less can be
used, and as a hard solder, a silver brazing material, copper brazing
material, or nickel brazing material, and a soft aluminum solder and an
aluminum joining solder (for example, ALMIT-350 or the like) can be used.
The solder is a typical soft solder, and uses Pb--Sn-based alloy or the
like. For the structure of the present invention, a brazing material with
a melting point of 350 degrees centigrade or more is preferable, and a
soft solder such as a soft aluminum solder, and more preferably, a hard
solder can be used. Particularly, a metal which is of the same kind as
the metal contained in the metal impregnated carbon composite or a metal
which produces an alloy with high thermal conductivity and fracture
toughness are preferable. The structure relating to the present invention
can be obtained without greatly melting the metals of the metal substrate
and the metal impregnated carbon composite by performing joining by
melting said brazing material and making it flow into gaps. As an
alternative material of such a brazing material, a lamination of metal
foils of an aluminum foil, a tin foil, a copper foil, a silver foil,
etc., can also be used.

[0025] In the metal substrate-metal impregnated carbon composite structure
relating to the present invention, the brazing material is integrally
welded to the metal in the metal impregnated carbon composite, and shows
a so-called anchor effect by entering gaps of the composite, and has an
effect of strengthening the joining performed by integrating components.

[0026] In the metal substrate-metal impregnated carbon composite structure
relating to the present invention, when the thickness of the entire
structure of the metal impregnated carbon composite and the copper or
aluminum substrate is about 1 millimeter or more, the thickness ratio of
the metal impregnated carbon composite to the metal substrate is 1 of the
composite to about 2 or more of the metal substrate, and preferably, 1 to
3. At this ratio, warp of the structure processed at the above described
temperature and pressure is controlled to be 0.15 millimeters or less on
the diagonal line of 50 millimeters×50 millimeters, and
particularly preferably, warp is controlled to 0.05 millimeters or less
on the diagonal line of 50 millimeters×50 millimeters.

[0027] The metal substrate-metal impregnated carbon composite structure of
the present invention has a heat stress relaxing effect in its mounting
portion, and properties of a high thermal conductivity, and a small
thermal expansion coefficient. As the metal impregnated carbon composite,
a composite having properties of a thermal conductivity of 100 W/mK or
more, a thermal expansion coefficient of 4 to 15×10-6/degrees
centigrade, and a Young's modulus of 25 GPa or less is selected. This
metal impregnated carbon composite is anisotropic, so that one direction
of the surface is controlled so as to have these values of the properties
of the thermal expansion coefficient and Young's modulus, and that the
thickness direction or the surface direction is controlled so as to have
these values of the properties of the thermal conductivity.

[0028] Next, a production method for the metal substrate-metal impregnated
carbon composite structure of the present invention will be described.

[0029] The production method for the metal substrate-metal impregnated
carbon composite structure of the present invention is performed by
brazing and soldering by using a brazing material, and in detail,
includes the steps of interposing a brazing material between copper or
aluminum as a metal substrate and a metal impregnated carbon composite
and holding it at a high temperature, forming a joining layer by melting
the brazing material and making it flow into gaps, and cooling it at
least under pressurization, whereby providing a metal substrate-metal
impregnated carbon composite structure suitable as a heat radiation
substrate with smaller warp. The pressurizing condition is not always
necessary in the joining layer forming step, however, in the cooling
step, it is essential.

[0030] As a temperature in the joining, a temperature which sufficiently
melts the brazing material, lowers the yield stress of the aluminum or
copper substrate, and realizes reduction in warp by means of pressurizing
is set. Normally, a temperature equal to or more than the melting point
of the brazing material is adopted. In the brazing and soldering method
in the production method of the present invention, in the case of an
aluminum substrate, a method involving soldering such as high-temperature
soldering is also included. The aluminum or copper substrate and the
metal impregnated carbon composite are joined due to an anchor effect
obtained by welding of the melted brazing material to the metal of the
composite and entering of the melted brazing material into gaps of the
metal impregnated carbon composite by means of pressurizing, so that a
temperature of 500 to 610 degrees centigrade in the case of the aluminum
substrate and a temperature of 500 to 850 degrees centigrade in the case
of the copper substrate are preferable, however, optimal temperatures may
be selected according to the pressurizing condition, etc.

[0031] As an especially preferable temperature, in the case of a metal
impregnated carbon composite impregnated with aluminum, a temperature
near 630 degrees centigrade at which the impregnating aluminum does not
flow out from the composition of the composite is a maximum temperature.
In the case of a metal impregnated carbon composite impregnated with
copper, a temperature of 950 degrees centigrade becomes the maximum
temperature due to the yield stress of copper when the substrate made of
copper is used, and a temperature near 630 degrees centigrade becomes the
maximum temperature for the same reason when the substrate made of
aluminum is used.

[0032] The metal impregnated carbon composite is low in tensile strength
although being high in compression rupture strength. To the metal
impregnated carbon composite of the substrate joined while pressurized, a
stress is applied in the compression direction. When an element or part
is soldered, a stress acts in the tension direction on the metal
impregnated carbon composite, and to apply the compression stress to the
metal impregnated carbon composite even in this state, the joining
temperature is desirably as high as possible.

[0033] The pressurizing operation is preferably performed during melting
of the brazing material since the main component of the composite is
carbon that is hardly wetted with metal and its surface roughness is
high.

[0034] To obtain a substrate with smaller warp, the pressurizing pressure
is preferably set to 0.2 MPa to 30 MPa in the case of an aluminum
substrate and 3 MPa to 50 MPa in the case of a copper substrate as a
pressurizing condition on a level that does not cause great plastic
deformation of the aluminum substrate or copper substrate, however,
joining is still possible even at a pressure lower than described above.

[0035] The metal impregnated carbon composite to be used as a constituent
of the metal substrate-metal impregnated carbon composite structure of
the present invention, uses a carbon material as a base material and
contains a metal component. As the metal component, magnesium, aluminum,
copper, silver, and alloys of these metals can be used. Such metal
impregnated carbon composite is not especially limited as long as it
contains a metal component dispersed in a carbon component, and for
example, a metal impregnated carbon composite obtained by impregnating a
carbon material with a metal component at a high pressure or in vacuum
(metal impregnation method), a metal impregnated carbon composite
obtained by kneading a particulate carbon material and metal component
and forging these (particle sintering method), and a composite obtained
by molding carbon or carbon fibers subjected to surface treatment with a
metal at a high temperature and a high pressure (high-temperature
high-pressure method), and the like can be used.

[0036] Furthermore, a metal impregnated carbon composite obtained by
pressure-filling or impregnating a carbon mold with a porosity of 35% or
more containing graphite particles or carbon fibers that are described in
Japanese Patent Publication No. 3351778, with aluminum, copper, or alloys
of these by means of liquid forging, can also be used.

[0037] Such a metal impregnated carbon composite preferably contains a
metal component of 50% or less in terms of volume in all materials, and
preferably, 80% or more of the capacities inside gaps or pores of the
carbon material are filled. The thermal conductivity, thermal expansion
coefficient, and elastic modulus of the metal impregnated carbon
composite depends on the kind of the metal component contained, however,
when the metal component is copper, silver, or alloys of these, a
composite with a thermal conductivity of 100 W/mK or more in the
thickness direction, a thermal expansion coefficient of
4×10-6/degrees centigrade to 12×10-6/degrees
centigrade, and an elastic modulus of 250 GPa or less in the surface
direction can be realized, and when the metal component is aluminum or an
aluminum alloy, a composite with a thermal conductivity of 100 W/mK or
more in the thickness direction, a thermal expansion coefficient of
4×106/degrees centigrade to 8×106/degrees
centigrade, and a Young's modulus of 25 GPa or less in the surface
direction can be obtained.

[0038] The metal impregnated carbon composite is normally porous, so that
a plating failure may occur or an error may occur in an air tightness
test in an exposed portion. As a measure against this, it is necessary
that the metal impregnated carbon composite is housed in a counterbore of
the aluminum or copper substrate, and the substrate surface and the
entire surface of the metal impregnated carbon composite are covered by a
metal foil or their ends are covered by a metal foil by using a brazing
material or the like.

[0039] The surface of the metal substrate-metal impregnated carbon
composite structure of the present invention is finished by nickel
plating or the like for mounting semiconductors of silicon, etc., or
electronic parts or for corrosion proofing. If necessary, the structure
to which a ceramic circuit is joined can be provided.

[0040] FIG. 1 shows a detailed example of a basic structure of the metal
substrate-metal impregnated carbon composite structure of the present
invention. In the drawing, the structure including a metal impregnated
carbon composite 3 joined to the upper surface of an aluminum or copper
substrate 4 as a metal substrate via a brazing material 3' is the metal
substrate-metal impregnated carbon composite structure A of the present
invention. FIG. 1 shows a construction in which an electronics device
including a silicon element or ceramics substrate 1 is mounted on the
upper surface of a metal impregnated carbon composite 3 via a solder 2.

[0041] FIG. 2 shows a construction in which the upper surface of the metal
substrate-metal impregnated carbon composite 3 shown in FIG. 1 is covered
by a metal foil 5.

[0042]FIG. 3 shows an application example of the metal impregnated carbon
composite structure of the present invention to a CPU cap, wherein an
aluminum or copper substrate 4 and a metal impregnated carbon composite 3
are joined via a brazing material 3'.

[0043] FIG. 4 is a sectional view of a structure in which upper and lower
surfaces of a metal impregnated carbon composite 3 joined within a frame
of an aluminum or copper substrate 4 are covered by metal foils 5 via a
brazing material 3'.

[0044]FIG. 5 illustrates a basic layout of units in a hot press furnace
for producing the metal substrate-metal impregnated carbon composite
structure of the present invention. In the drawing, the reference symbol
A denotes a metal substrate of the present invention, and above and below
this, spacers 7 are disposed, respectively, and the substrate is pressed
against a receiving base 8 by a ram 6 under predetermined conditions.

EXAMPLES

[0045] Hereinafter, the present invention will be described in greater
detail based on examples and comparative examples. Of course, the present
invention is not limited by the examples.

[0046] For performance evaluation of the metal substrate-metal impregnated
carbon composite structure, etc., the following measuring methods were
used.

(1) Warp Measurement

[0047] A projecting portion on the diagonal line on the metal impregnated
carbon composite side of a sample piece was measured by using a
three-dimensional non-contact laser measuring device (distributed by
Sigma Koki Co., Ltd., using a three-dimensional shape measuring program
made by COMS Co., Ltd.)

(2) Thermal Conductivity.

[0048] Thermal conductivity was obtained as a product of a thermal
diffusion factor, specific heat, and density. The thermal diffusion
factor was measured by using TC-7000 made by ULVAC-RIKO, Inc., according
to a laser flash method. As an irradiation beam, a ruby laser beam
(excitation voltage: 2.5 kV, uniform filter and dimming filter: one) was
used.

(3) Thermal Expansion Coefficient

[0049] The thermal expansion coefficient was measured from a room
temperature to 300 degrees centigrade by using a heat analyzer 001,
TD-5020 made by MAX Science.

Example 1

[0050] A: copper foil with a thickness of 0.02 millimeters, B: a product
with a thickness of 0.5 millimeters (SZ500 made by Sentan Zairyo Co.,
Ltd.) obtained by impregnating a unidirectional carbon fiber/carbon
composite with copper, and C: copper C1020 with a thickness of 2
millimeters were prepared in a size of 50 millimeters×50
millimeters respectively. As the joining layer, a metal foil of a
combination of a 0.01 mm tin foil and a 0.02 mm copper foil was inserted
between A and B and between B and C, and set in the hot press. The set
materials were held in a vacuum atmosphere at a temperature of 800
degrees centigrade for 30 minutes, and pressurized at 20 MPa and cooled
when holding was finished. Warp of the trial product projected toward the
composite side and was 0.05 millimeters on the diagonal line of
substantially 50×50 millimeters.

Example 2

[0051] A: copper foil with a thickness of 0.02 millimeters, B: a product
with a thickness of 1 millimeter (SZ500 made by Sentan Zairyo Co., Ltd.)
obtained by impregnating a unidirectional carbon fiber/carbon composite
with copper, and C: copper C1020 with a thickness of 1 millimeter were
prepared in a size of 50 millimeters×50 millimeters respectively. A
metal foil of a combination of a 0.01 mm tin foil and a 0.02 mm copper
foil was inserted as a joining layer between A and B and between B and C,
and set in the hot press. The inside of the hot press was held in a
vacuum atmosphere at a temperature of 800 degrees centigrade for 30
minutes, and when holding was finished, the materials were pressurized at
20 MPa then cooled, and warp of a thus obtained trial product projected
toward the composite side and was 0.12 millimeters on the diagonal line
of substantially 50×50 millimeters.

[0052] When observing the cross section of the composition at a
magnification of 600, copper in the composite, the brazing material, and
the copper substrate were integrated, and no defects such as cracks and
gaps in the joined surface were found. When externally observing this
trial product after re-heating this in a nitrogen gas at 700 degrees
centigrade for two hours and then cooling it, breakage such as separation
of the copper foil and substrate and an increase in warp were not
observed.

Example 3

[0053] The trial product manufactured on trial in Example 2 was divided
into two, and on the copper foil upper central portion of each divided
trial product, a kovar-made flange (external dimensions: 12.7
mm×20.8 mm, plate thickness: 1 mm) whose bottom was applied with
silver brazing material BAg-7 was installed and a weight of about 2 kg
was placed thereon, and the flange was joined at 760 degrees centigrade.
Warp on the diagonal line of 30×20 millimeters on the copper
substrate side was 0.02 millimeters, and warp did not greatly change
before and after the flange was joined. The same flange-joined trial
product was subjected to a simple heat cycle test ten times on a hot
plate heated to 350 degrees centigrade for 5 minutes and on an iron base
(normal temperature) with high heat capacity for 10 minutes, however,
separation of the flange was not observed.

[0054] As described above, based on the fact that a kovar-made flange
(thermal expansion coefficient: about 5×10-6/degrees
centigrade at 30 degrees centigrade to 40 degrees centigrade) could be
joined to the metal substrate-metal impregnated carbon composite
structure of the present invention and it was not broken even by a simple
heat cycle test, it was proven that the thermal stress relaxing effect
was brought about.

Example 4

[0055] B: a product with a thickness of 1 millimeter (SZ300 made by Sentan
Zairyo Co., Ltd.) obtained by impregnating a carbon material with
aluminum, and C: aluminum A1050 with a thickness of 3 millimeters were
prepared in a size of 50 millimeters×50 millimeters respectively. A
0.3 mm sheet of A4047 (Al alloy, the same applies to the following
description) was inserted as a joining layer between A and B and set in
the hot press. The inside of the hot press was held in a nitrogen
atmosphere at a temperature of 600 degrees centigrade for 30 minutes, and
when holding was finished, the materials were pressurized at 15 MPa then
cooled, and warp of a thus obtained trial product projected toward the
composite side and was 0.03 millimeters on the diagonal line of
substantially 50×50 millimeters.

Example 5

[0056] A: a 96%-alumina substrate with a thickness of 0.6 millimeters, B:
a product with a thickness of 0.5 millimeters (SZ300 made by Sentan
Zairyo Co., Ltd.) obtained by impregnating a carbon material with
aluminum, and C: aluminum A1050 with a thickness of 3 millimeters were
prepared in a size of 50 millimeters×50 millimeters respectively.
As a joining layer, a 0.3 mm sheet of A4047 was inserted between A and B
and between B and C, and set in the hot press. The materials were held in
a nitrogen atmosphere at a temperature of 600 degrees centigrade for 30
minutes, and when holding was finished, pressurized at 15 MPa and cooled.
Warp of the trial product projected toward the alumina side and was 0.15
millimeters on the diagonal line of 50×50 millimeters. The same
trial product was subjected to a simple heat cycle test ten times on a
hot plate heated to 350 degrees centigrade for 5 minutes and on an iron
base (normal temperature) with high heat capacity for 10 minutes,
however, no abnormality was found. The warp did not change before and
after the cycle test.

[0057] As described above, based on the fact that an alumina substrate
(thermal expansion coefficient: about 8×10-6/degrees
centigrade at RT-800 degrees centigrade) could be joined to the metal
substrate-metal impregnated carbon composite structure of the present
invention and it was not broken even by a simple heat cycle test, so that
it was proven that the heat stress relaxing effect was brought about.

Comparative Example 1

[0058] B: a product with a thickness of 0.5 millimeters (SZ300 made by
Sentan Zairyo Co., Ltd.) obtained by impregnating a carbon material with
aluminum, and C: aluminum A1050 with a thickness of 3 millimeters were
prepared in a size of 50 millimeters×50 millimeters respectively.
As a joining layer, a 0.3 millimeters sheet of A4047 was inserted between
A and B, a weight of 10 kg was placed thereon, and the materials were
joined by held in a nitrogen atmosphere at a temperature of 595 degrees
centigrade for 30 minutes. Warp of the trial product projected toward the
composite side and was 0.2 millimeters on the diagonal line of
substantially 50×50 millimeters, however, the materials were easily
separated from each other when separated from the ends of the trial
product after inspection.

Comparative Example 2

[0059] A: a 96%-alumina substrate with a thickness of 0.6 millimeters and
C: aluminum A1050 with a thickness of 3 millimeters were prepared in a
size of 50 millimeters×50 millimeters respectively. As a joining
layer, a 0.3 millimeters sheet of A4047 was inserted between A and C, and
set in the hot press. It was held in a nitrogen atmosphere at a
temperature of 595 degrees centigrade for 30 minutes, and when holding
was finished, the product was pressurized at 15 MPa and cooled. Warp of
the trial product projected toward the alumina side and was over 0.3
millimeters (unmeasurable) on the diagonal line of substantially
50×50 millimeters, and the alumina substrate was cracked.

Comparative Example 3

[0060] A: a 96%-alumina substrate with a thickness of 0.6 millimeters, B:
a product (SZ300 made by Sentan Zairyo Co., Ltd.) with a thickness of 0.5
millimeters obtained by impregnating a carbon material with aluminum, and
C: aluminum A1050 with a thickness of 3 millimeters were prepared in a
size of 50 millimeters×50 millimeters respectively. As a joining
layer, a 0.3 millimeters sheet of A4047 was inserted between A and B and
between B and C, and set in the hot press. The materials were held in a
nitrogen atmosphere at a temperature of 620 degrees C. for 30 minutes,
and while being held, pressurized at 50 MPa and cooled. The 3
millimeters-thick aluminum substrate expanded by 0.3 millimeters or more
to the left and right, and alumina and the composite semi-fused and sunk
under the aluminum substrate, and caused deformation.

Comparative Example 4

[0061] A trial product was prepared under the same conditions by the same
operations as in Example 2 except that the pressurizing condition was set
to 0.04 MPa instead of 20 MPa. Warp of this trial product projected
toward the composite side and was over 0.15 millimeters on the diagonal
line of substantially 50 millimeter×50 millimeters. The central
portion was joined, however, four corners were not joined.

Comparative Example 5

[0062] A trial product was prepared under the same conditions by the same
operations as in Example 4 except that the pressurizing condition was set
to 0 MPa instead of 15 MPa. Warp of this trial product projected toward
the composite side and was over 0.2 millimeters on the diagonal line of
substantially 50 millimeters×50 millimeters. The central portion
was joined, however, four corners were not joined.

[0063] A metal substrate-metal impregnated carbon composite structure of
the present invention is controlled in warp caused by joining, and is
also improved in strength, so that it is useful as a heat radiation
material. Therefore, it can be widely used for power module substrates,
laser diode parts (spacers, carriers), LED substrates, plastic PKG heat
spreaders, printed boards, inverter substrates, etc., as well as IC
packages, and in particular, offers a great contribution as a heat
radiation material for electronics devices.

BRIEF DESCRIPTION OF THE DRAWINGS

[0064] [FIG. 1] is a schematic view showing a basic structure of a metal
substrate-metal impregnated carbon composite structure of the present
invention;

[0065] [FIG. 2] is a schematic view of a metal substrate-metal impregnated
carbon composite structure of the present invention in which the metal
impregnated carbon composite is covered by a metal foil;